Besides the corrections others have said, I really can’t think of any reason people would intentionally use legacy BIOS on a machine with UEFI for a new install.
Like, I could get doing it for an old install - I know someone who installed Windows 7 in 2015 on their then-new desktop build and later upgraded to 10 but is stuck on legacy BIOS for now with that machine because 7 only ran on that.
I could see something similarly jank happening to someone in the Linux world and then decide not to address it for “if it ain’t broke, don’t fix it reasons”, but certainly not for no reason.
It’ll definitely be a difficult undertaking, but I plan on really trying to have a 5.25” bay when I build another PC.
That probably won’t be for a couple more years, though. I’m on a Ryzen 5 2600 and RX 580, and I really don’t do that much intense gaming; a GPU upgrade is tempting so I can actually use ROCm for some casual Blender Cycles renders, though. I hope that the already dismal supply of those 5.25 cases doesn’t dwindle even more.